The present invention relates to image data processing method, program, system, and various devices such as a printing data creating apparatus, an inkjet printing apparatus employing such method, program and system.
Conventionally, an inkjet printing apparatus has been well known and widely used. The inkjet printing apparatus is typically configured such that ink is directed from an ink supplying source to a plurality of ink ejection channels of an inkjet head, and, by selectively driving actuators such as heater elements or piezoelectric elements, a jet of ink is ejected from ejection nozzles provided at the tip of the ejection channels.
In order to produce a color image, for each of the pixels making up the color image, the color is divided into three primary colors of, for example, cyan (C), magenta (M), yellow (Y), and then ink having each color is ejected with the density thereof being adjusted based on the density of the corresponding color component. As the density-adjusted color inks are mixed, the pixel of the color image is produced.
A black pixel is formed as a mixed color which is a mixture of the three primary colors having the maximum densities, respectively. Since black color recreated as the mixed color tends to be dull black, or unclear due to its low contrast. Therefore, black (K) ink is generally ejected to recreate black color for a black pixel or pixels which contain black color as color component.
Incidentally, after the ink is ejected onto a recording sheet and before permeates into the sheet, neighboring ink having different colors may mix to cause a blot. Since black ink has especially much color difference from the primary color ink (cyan, magenta, yellow), the blot comes into prominence so that quality of the printed image is deteriorated.
U.S. Pat. Nos. 6,084,604 and 6,312,102 disclose method and apparatus for suppressing the above deficiency, teachings of which are incorporated herein by reference. According to the disclosure of the above patents, when a black pixel is to be formed next to color pixels, black ink is not used and the black pixel is formed using the mixed color ink.
Japanese Patent Provisional Publication No. 2000-118007 discloses method and apparatus which distinguishes skeleton pixels from contour pixels in a solid area, and ejecting more ink for the skeleton pixels, while less ink for the contour pixels, thereby blots can be reduced at the boundary between the contour pixels and an unprinted area.
According to the method and apparatus disclosed in the above US patents, however, there is a problem. If the black ink is substituted with the mixture of the color inks, the total amount of the ink used for the black pixels increases and a longer time is required until the ink permeates into the recording sheet, and the blot may easily be cause. Besides, if adjoining color pixels have different colors and relatively high densities, the blot is easily formed. If the color difference between the pixels is relatively large, the bolt is significant.
According to the above-described JP publication, since only the area where the RGB gray-scale values are set to zero, that is, only the black area is regarded as the solid pixel area, the blot cannot be reduced when different color pixels of high densities lie next to each other.
Further to the blot between the color pixels described above, the following problem should also be considered.
When fabrics such as T-shirt are used as the recording medium, grooves are formed on a fabric surface depending on kinds and/or materials of the fabrics, and depending on the stitching methods including sewing, knitting and weaving. When the grooves are formed, the ink tends to bleed along the direction the grooves extend.
FIG. 15 is an enlarged view of an example of the fabric formed with the grooves. As shown in FIG. 15, a part of the knitted (woven) yarns which are raised on the surface is indicated in black, showing that the yarns are knitted (woven) in the direction from the lower left to the upper right in the drawing. The grooves produced between the yarns are indicated in white. Those grooves are also formed in the direction from the lower left to the upper right in the drawing. When printing is carried out on the fabric such as T-shirt, the ink moves more, after having been ejected onto the fabric, in the direction where the grooves extend, than other directions on the fabric. Accordingly, the ink tends to bleed along the direction in which the grooves extend (the direction from the lower left to the upper right in FIG. 15). The aforementioned prior art was intended to reduce the blot of the neighboring ink, but not intended to reduce the bleeding caused due to the reason peculiar to the fabric.